[R.O. 1988 § 15-20; Ord. No. 3500 § 2, 4-1-2002]
Stormwater runoff and soil erosion can be controlled and minimized through the regulation of stormwater runoff from development sites. Proper management of stormwater runoff will minimize damage to public and private property, reduce the effects of development on land, control stream channel erosion, reduce local flooding, and maintain after development, as nearly as possible, the predevelopment runoff characteristics.
[R.O. 1988 § 15-21; Ord. No. 3500 § 2, 4-1-2002]
The purpose of this Article is to establish general requirements and principles for the design and construction of stormwater conveyance systems and detention facilities within the City of Rolla.
[R.O. 1988 § 15-22; Ord. No. 3500 § 2, 4-1-2002]
The stormwater improvement plan shall include the following information:
(a) 
A schedule estimating the dates of completion of construction for all storm drainage facilities shown on the plan;
(b) 
All necessary construction specifications;
(c) 
Basic design criteria, including the rainfall intensity, percentage of imperviousness, runoff coefficients for each tributary basin area in the drainage area, time of concentration, peak flow rates, and any other pertinent design criteria;
(d) 
A vicinity map;
(e) 
Key map of the entire project to scale, showing easements, sewer lines and facilities, both existing and to be constructed;
(f) 
A drainage area map showing the ridge line of the area tributary to each inlet, sewer, and channel section in the system. The map shall be labeled with or accompanied by a table summarizing the basic design criteria. The established elevations, gradients and contours of the finished graded surfaces and streets shall be shown in support of the inlet drainage area lines and indicated directions of flow;
(g) 
A subdivision plat, dimensioned and substantially complete and ready for filing;
(h) 
Recorder of Deeds book and page from Phelps County Recorder of Deeds for existing recorded easements when not part of a recorded subdivision plat;
(i) 
All existing and proposed easements and rights-of-way;
(j) 
Plans and profiles of each storm drain, showing location, size, design flow, flow line elevations, gradients and materials; boring information and rock elevations along the proposed storm drain anywhere applicable; location, depths and sizes of adjacent or crossing sewer lines and utilities; and special construction requirements such as concrete cradle or encasement, backfill, size and class of pipe. Typical cross sections of swales, ditches or open channels;
(k) 
Summary design information for each component of the stormwater conveyance system;
(l) 
All elevations shall be based upon USGS datum with location of the benchmark indicated on the plans. Acceptable benchmarks include those established by the City of Rolla, Missouri Department of Transportation and the United States Geological Survey;
(m) 
Details of special structures, channel improvements, culverts, transitions, headwalls, aprons and junction chambers, all adequately detailed and dimensioned, including placement of steel in reinforced concrete structures;
(n) 
The location of all utilities anticipated to be encountered during construction shall be shown. Plans must be submitted to all utility companies for verification of conflicts. Storm and sanitary sewers shall be located to comply with State laws and regulations governing such placement;
(o) 
Location of all existing and proposed building facilities with minimum floor elevations where buildings could be impacted by floodwaters and location of all existing and proposed utilities on the site;
(p) 
For design of detention facilities, calculations of peak runoff flows shall be provided for all areas which are tributary to the location of the proposed detention facility for both existing conditions and conditions after the planned development of the site. The information shall include the acreage of all areas contributing flow to the site and the present land use by acreage of those areas.
[R.O. 1988 § 15-23; Ord. No. 3500 § 2, 4-1-2002]
(a) 
The improvements shall be in accordance with the City of Rolla stormwater design standards and must be prepared by a registered professional engineer.
(b) 
These stormwater improvements should seek to utilize pervious areas for stormwater treatment and to infiltrate stormwater runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas to the maximum extent practicable.
(c) 
These stormwater improvements shall maintain the peak rate of surface water runoff which flows from any specific site during and following development so that the peak rate of runoff will not exceed the pre-project conditions to the maximum extent practicable. The effects of the proposed development on stormwater discharge to downstream locations shall be determined and:
(1) 
Sufficient information showing locations of downstream watercourses, channels, sewers, culverts, structures and adjoining land shall be provided;
(2) 
The need for special storm drainage easement requirements to locations downstream of the proposed development and/or downstream drainage modifications or protection shall be evaluated.
(d) 
The design capacity for all stormwater conveyance systems and detention facilities shall meet the following specifications:
(1) 
All stormwater conveyance systems shall be designed to accommodate peak flows from a ten-year design storm;
(2) 
All detention facilities shall be designed to detain the runoff from design storms up to and including a twenty-five-year design storm. Such facilities shall be designed to release the retained surface water runoff such that the peak rate of runoff from the tract after development shall not exceed the peak rate of runoff from the tract prior to development for the two-, ten- and twenty-five-year design storms.
(3) 
Detention facilities should be designed to accommodate peak retention with at least one (1) foot of freeboard.
(e) 
Stormwater improvements shall be designed and implemented such that all buildings and other structures shall be protected from the floodwaters of a one-hundred-year design storm. The stormwater improvement system shall also pass the floodwaters of a one-hundred-year design storm without damage to either the conveyance system or the detention facilities.
(f) 
Open channels shall be located in drainage easements sufficiently wide to accommodate a one-hundred-year design storm and shall be designed and constructed in such a manner as to provide easy maintenance of the channel and side slopes and to prevent erosion from the design flows. If the channel extends between buildings, consideration must be given to adequate protective measures, such as paving the channel invert and side slopes, bank protection or fencing. Open channels in residential areas shall generally be located along the rear or side lot lines.
(g) 
Where storm drainage along the side lot lines of residential property is to be in conduit, the conduit shall extend to a point at least forty (40) feet to the rear of the front building line or ten (10) feet beyond the rear line of the structure, whichever is greater. A surface swale shall be provided over this area to contain at least a one-hundred-year storm. At the point of intersection with the open channel, some type of facility shall be provided to disperse flow and minimize erosion.
(h) 
Where culverts are placed under roadways, they shall extend to at least the limits of the right-of-way or the toe of the roadway embankment, whichever is greater, and proper measures shall be taken to prevent erosion. Embankments shall be protected to prevent erosion against a one-hundred-year storm.
(i) 
Curb inlets shall be installed at or near intersections where they are deemed necessary for the safety of pedestrian and vehicular traffic. No curb inlet shall be located within a crosswalk.
(j) 
All detention facilities shall include an emergency or overflow spillway which will pass excess flows greater than those of the twenty-five-year design storm. The emergency spillway shall be designed to safely pass the flow resulting from the one-hundred-year design storm without damage to the basin.
(k) 
Modifications to the stormwater improvement plan shall be processed and approved or disapproved in the same manner as Section 15-8 of this Chapter.
[R.O. 1988 § 15-24; Ord. No. 3500 § 2, 4-1-2002]
All stormwater conveyance, detention and erosion control design shall meet the provisions of this Chapter and shall comply with the latest revision of The stormwater design standards for the City of Rolla filed in the office of the Director of Public Works.
[R.O. 1988 § 15-25; Ord. No. 3500 § 2, 4-1-2002]
(a) 
Waivers For Providing Stormwater Conveyance Systems. Every developer shall provide for an on-site stormwater conveyance system. No waivers shall be approved.
(b) 
Substitutions For Providing Stormwater Detention. Every developer shall provide for stormwater detention unless the City determines that detention may not be appropriate for the development. In cases where the City determines that detention is not appropriate, the developer shall be required to substitute cash payments in lieu of stormwater detention requirements. The minimum requirements for stormwater detention may be waived in whole upon request of the developer, provided that all of the following conditions apply:
(1) 
It can be demonstrated that the proposed development is not likely to impair attainment of the objectives of this Chapter.
(2) 
The proposed development is equal to or less than twenty (20) acres for residential development and/or one (1) acre for commercial or industrial development; or, the proposed development is projected to have an increase in peak stormwater runoff for a ten-year design storm of no more than five (5) cfs; or, if the City of Rolla determines that an off-site regional detention facility would be favorable to the proposed on-site detention facility. At the request of the City, submittal of hydraulic analyses comparing on-site and off-site options for detention may be required.
(3) 
Provisions are made to manage stormwater detention by an existing or future proposed off-site regional facility. The off-site regional facility is required to be adequately sized to provide a level of stormwater control that is equal to or greater than that which would be afforded by on-site local detention and has a legally obligated entity responsible for long-term operation and maintenance of the detention facility.
[R.O. 1988 § 15-26; Ord. No. 3500 § 2, 4-1-2002]
(a) 
Where the City of Rolla determines not to require stormwater detention, the developer shall be required to pay a fee in lieu of on-site stormwater detention. This fee shall be based on an increase in the peak stormwater flow from the development in question.
(b) 
For subdivisions zoned R-1 and R-2, this fee shall be in the amount of five hundred dollars ($500.00) for each acre of property in the development, with a minimum payment of five hundred dollars ($500.00). For subdivisions zoned R-3, R-4, C-1, C-2, C-C, and M, this fee shall be in the amount of one thousand five hundred dollars ($1,500.00) for each acre of property in the development, with a minimum payment of one thousand five hundred dollars ($1,500.00).
(c) 
All of the monetary contributions shall be credited to the City of Rolla's Stormwater Improvement Fund, and shall be made by the developer prior to the issuance of any land development permit for the development.